Method and device for controlling congestion in mobile communication system

ABSTRACT

The present invention relates to a method and a device for controlling congestion in a mobile communication system. A method for controlling congestion of a network node according to the present invention comprises the steps of: receiving congestion-related information from at least one base station; transmitting a user equipment information request message for making a request for information on a piece of user equipment corresponding to the base station to a mobility management entity; receiving a user equipment information response message including the information on the user equipment corresponding to the base station from the mobility management entity; and transmitting the information on the piece of user equipment corresponding to the base station to another core network node.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.15/106,798 filed on Jun. 20, 2016, which is a 371 of InternationalPatent Application No. PCT/KR2014/012643 filed on Dec. 22, 2014, whichclaims priority to Korean Patent Application Nos. 10-2013-0160558 filedon Dec. 20, 2013, 10-2014-0096529 filed on Jul. 29, 2014 and10-2014-0155666 filed on Nov. 10, 2014, the disclosures of which areherein incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a mobile communication network, andmore particularly to a method and device for controlling congestion.

BACKGROUND

Mobile communication systems have primarily been developed to providevoice communication services while guaranteeing user mobility. Mobilecommunication systems have gradually extended the communication servicearea thereof to high-speed data communication services in addition tovoice communication services. However, due to a lack of resources and ademand for higher-speed communication services from users in currentlyavailable mobile communication systems, an enhanced mobile communicationsystem is required.

To meet such requirements, Long Term Evolution (LTE), as onenext-generation mobile communication system under development, is beingstandardized in the 3rd Generation Partnership Project (3GPP). LTE istechnology for implementing high-speed packet-based communication at atransfer rate of up to about 100 Mbps. Several methods are beingdiscussed to implement high-speed packet-based communication. Examplesof such methods include reducing the number of nodes on a communicationpath by simplifying the architecture of a network and maximallyapproximating radio protocols to radio channels.

FIG. 1 is a view illustrating the structure of a typical LTE mobilecommunication system.

Referring to FIG. 1, a radio access network of an LTE mobilecommunication system may include next-generation base stations (EvolvedNode Bs, EUTRAN, hereinafter referred to as eNBs or Node Bs) 110, aMobility Management Entity (MME) 120 and a Serving Gateway (S-GW) 130.

A piece of user equipment (hereinafter, referred to as a UE) 100accesses an external network via an eNB, the S-GW, and a P-GW (PDNGateway (Packet Data Network Gateway)).

The eNB 110, which is a Radio Access Network (RAN) node, corresponds tothe Radio Network Controller (RNC) of the Universal Terrestrial RadioAccess Network (UTRAN) system and the Base Station Controller (BSC) ofthe GSM EDGE Radio Access Network (GERAN) system. The eNB 110 connectsto the UE 100 over a radio channel and performs a function similar tothat of the legacy RNC/BSC. The eNB may use several cells at the sametime.

In LTE, not only real-time services such as VoIP (Voice over IP) usingthe Internet protocol, but also all user traffic are provided over ashared channel. Accordingly, a device to perform scheduling bycollecting status information of UEs is needed, and the eNB serves asthis device.

The MME 120 is responsible for various control functions. One MME mayconnect to multiple eNBs.

The S-GW 130, which is a device for providing a data bearer, iscontrolled by the MME 120 to generate or delete a data bearer.

The core network of the LTE mobile communication system may furtherinclude nodes such as an Application Function, a PCRF and a P-GW (notshown) in addition to the MME 120 and the S-GW 130.

The Application Function (AF) is a device for exchangingapplication-related information with a user at the application level.

The PCRF (Policy Charging and Rules Function) is a device forcontrolling a policy associated with the Quality of Service (QoS) forthe user, and a PCC (Policy and Charging Control) rule corresponding tothe policy is delivered to the P-GW and applied. The PCRF (PolicyCharging and Rules Function) is an entity for comprehensivelycontrolling QoS and charging for traffic.

A path connecting the UE 100 to a RAN node 110, the RAN node 110 to theS-GW 130, and the S-GW 130 to a P-GW 160, through which user data istransmitted/received is generally referred to as a user plane (UP). In aUP path, a link between the UE 100 and the RAN node 110 uses a radiochannel subjected to heavy resource restriction.

In a wireless communication system such as LTE, QoS may be applied inunits of Evolved Packet System (EPS) bearers. One EPS bearer is used totransport IP flows having the same QoS requirements. QoS-relatedparameters may be designated for the EPS bearer. The QoS-relatedparameters include a QoS Class Identifier (QCI) and an Allocation andRetention Priority (ARP). The QCI is a parameter that defines a QoSpriority with an integer, and the ARP is a parameter to determinewhether to allow or reject generation of a new EPS bearer.

The EPS bearer corresponds to a Packet Data Protocol (PDP) context in aGeneral Packet Radio Service (GPRS) system. One EPS bearer belongs to aPDN connection, which may have an Access Point Name (APN) as anattribute. To generate a PDN connection for an IP Multimedia Subsystem(IMS) service such as Voice over LTE (VoLTE), a well-known IMS APN needsto be used.

To support voice calls in the LTE network, IMS-based VoLTE may be usedaccording to a Packet Switched (PS) scheme, or CS fall back (CSFB)reusing a Circuit Switched (CS) scheme of the 2G/3G system may be used.In the LTE network, VoLTE may be a term having the same concept as Voiceover IMS (VoIMS).

In a wireless communication system, particularly, the LTE system, whenan incoming or outgoing voice call occurs while a UE is using an LTEnetwork, a CSFB process of switching to a Circuit Switched (CS) networkis performed for a voice service. In this case, a separateauthentication procedure for the UE needs to be performed, and thusdelay may occur in providing the voice service. In general, the 2G/3Gsystem is a CS network capable of providing a CS service, and an entityresponsible for a control operation related to the CS service isreferred to as an MSC or VLR. In LTE, CSFB providing a switchingfunction for the CS service is performed between the MSC/VLR and the MMEby utilizing an SGs interface. If congestion occurs in a Radio AccessNetwork (RAN), the occurrence is preferably signaled to a Core Network(CN) to perform further optimized traffic processing.

To apply traffic control for each UE, bearer or service according tocongestion, the CN needs to recognize UEs located in a RAN in whichcongestion is occurring.

SUMMARY

The present invention is provided to solve the above problems and aimsto provide a method and device for effectively controlling congestion ina mobile communication system.

Specifically, the present invention aims to provide a method and devicefor acquiring, by a CN node of a mobile communication system, anidentifier of a UE located in a cell in which congestion occurs andproviding the same to another CN node.

Additionally, the present invention aims to provide a method and devicefor reducing service delay which occurs due to the process of exchangeof authentication or security information that is necessary when a UEbeing provided with a specific service switches to another service.

In accordance with an aspect of the present invention, a method forcontrolling congestion by a core network node in a mobile communicationsystem is provided. The method may include receiving congestion-relatedinformation from at least one base station; transmitting, to a mobilitymanagement entity, a terminal information request message for requestinginformation about a terminal corresponding to the base station, based onthe congestion-related information; receiving a terminal informationresponse message containing the information about the terminalcorresponding to the base station from the mobility management entity;and transmitting the information about the terminal corresponding to thebase station to another core network node.

In accordance with another aspect of the present invention, a method forcontrolling congestion by a mobility management entity in a mobilecommunication system is provided. The method may include: receiving,from the core network node, a terminal information request message forinformation corresponding to at least one base station experiencingcongestion; checking information about a terminal corresponding to thebase station; and transmitting, to the core network, a terminalinformation response message containing the information about theterminal.

In accordance with another aspect of the present invention, a corenetwork node for controlling congestion in a mobile communication systemis provided. The core network node may include: a transceiver totransmit and receive a signal; and a control unit to control to receivecongestion-related information from at least one base station, transmit,to a mobility management entity, a terminal information request messagefor requesting information about a terminal corresponding to the basestation, based on the congestion-related information, receive a terminalinformation response message containing the information about theterminal corresponding to the base station from the mobility managemententity, and transmit the information about the terminal corresponding tothe base station to another core network node.

In accordance with another aspect of the present invention, a mobilitymanagement entity for controlling congestion in a mobile communicationsystem is provided. The mobility management entity may include: atransceiver to transmit and receive a signal; and a control unit tocontrol to receive, from the core network node, a terminal informationrequest message for information corresponding to at least one basestation experiencing congestion, check information about a terminalcorresponding to the base station and transmit, to the core network, aterminal information response message containing the information aboutthe terminal.

In accordance with another aspect of the present invention, a method forsupporting a security procedure for a terminal by a core network node ina mobile communication system is provided. The method may includegenerating CS security key-related information for the terminal to usein a circuit-switched fallback (CSFB) procedure, and transmitting thegenerated CS security key-related information to a control node of a CSdomain.

In accordance with another aspect of the present invention, a corenetwork node for supporting a security procedure for a terminal in amobile communication system. The core network node may include atransceiver to transmit and receive a signal to and from the terminal orany nodes of the mobile communication system, and a control unit tocontrol to generate CS security key-related information for the terminalto use in a circuit-switched fallback (CSFB) procedure and transmit thegenerated CS security key-related information to a control node of a CSdomain.

In accordance with another aspect of the present invention, a method forperforming a circuit-switched fallback (CSFB) procedure by a terminal ina mobile communication system is provided. The method may includesensing triggering of the CSFB, checking CS security key-relatedinformation and performing a call setup process for a circuit switcheddomain based on the CS security key-related information.

In accordance with another aspect of the present invention, a terminalconfigured to perform a circuit-switched fallback (CSFB) procedure in amobile communication system is provided. The terminal may include atransceiver to transmit and receive a signal to and from a base station,and a control unit to control to sense triggering of the CSFB, check CSsecurity key-related information and perform a call setup process for acircuit switched domain based on the CS security key-relatedinformation.

According to an embodiment of the present invention, information about acell or base station and UEs belonging thereto may be signaled to a corenetwork, and accordingly, congestion may be effectively controlled forrespective cells or base stations.

According to an embodiment of the present invention, CS security keyinformation which a UE can use after switching to a legacy network maybe pre-delivered to a CS CN node and stored by the CS CN node, andaccordingly when CSFB occurs for the UE, the UE is allowed to use thestored CS security key information. Therefore, separate authenticationor security-related signaling is unnecessary, and thus a call connectiontime may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating the structure of a typical LTE mobilecommunication system.

FIG. 2 is a flowchart illustrating a sequence of operations of a UE anda network in the process of registration of the UE in a PS domainaccording to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating a sequence of operations of a UE anda network performed when CSFB is triggered for the UE according toanother embodiment of the present invention.

FIG. 4 is a flowchart illustrating a sequence of operations of a UE anda network performed when CSFB is triggered for the UE according toanother embodiment of the present invention.

FIG. 5 is a flowchart illustrating a process of delivering CS securitykey information performed when an MCS managing a UE is changed,according to the present invention.

FIG. 6 is a flowchart illustrating a sequence of operations of a UE inan idle mode performed using SRDS when a CS-based service is needed forthe UE, according to an embodiment of the present invention.

FIG. 7 is a flowchart illustrating a sequence of operations of a UE inan idle mode and an LTE system performed when a CS-based service isneeded for the UE in using SRDS, according to another embodiment of thepresent invention.

FIG. 8 is a flowchart illustrating a sequence of operations of a UE andan LTE system performed using SRDS when a CS-based service is needed forthe UE in an idle mode, according to another embodiment of the presentinvention.

FIG. 9 illustrates a method for activating ULI reporting on a UE presentin a specific RAN according to an embodiment of the present invention.

FIG. 10 illustrates a method for activating ULI reporting on a UEpresent in a specific RAN according to another embodiment of the presentinvention.

FIG. 11 illustrates a method for activating RCI reporting on a UEpresent in a specific RAN according to another embodiment of the presentinvention.

FIG. 12 is a flowchart illustrating an operation of exchanging a messagebetween two network nodes to identify UEs located in a congested cell(or eNB) according to an embodiment of the present invention.

FIG. 13 is a flowchart illustrating an operation of exchanging a messagebetween two network nodes to identify UEs located in a congested cell(or eNB) and information on a PDN connection of each UE.

FIG. 14 is a flowchart illustrating a message exchange process foractivating notification to periodically receive UE information.

FIG. 15 is a block diagram illustrating the internal structure of a UEaccording to an embodiment of the present invention.

FIG. 16 is a block diagram illustrating the internal structure of a CNnode according to an embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in more detail with reference to the accompanying drawings.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like elements. A detaileddescription of well-known functions and configurations incorporatedherein may be omitted in order to avoid obscuring the subject matter ofthe present invention.

In describing embodiments of the present invention in detail, adescription will be mainly given of an OFDM-based wireless communicationsystem, particularly 3GPP EUTRA standard by way of example, but thepresent invention is also applicable to other communication systemshaving a technical background or channel type similar to that of thepresent invention within the scope of the present invention by applyinga slight modification to the present invention, which can be implementedby those skilled in the art.

The detailed description of embodiments of the present invention givenbelow mainly focuses on a circuit switched fallback (CSFB) process inwhich the UE switches from LTE to a CS network to secure a voiceservice. The present invention mainly aims to simplify anauthentication/security information process which is needed when a UEswitches from one system to another to secure a specific service. Thepresent invention is also applicable to other communication systemsservices having a technical background or channel type similar to thatof the present invention within the scope of the present invention byapplying a slight modification to the present invention, which can beimplemented by those skilled in the art.

In the specification and the drawings, the term LTE network adoptedherein may have the same meaning as E-UTRAN, and a CS network may be aUTRAN, GERAN, CDMA2000, or a network similar thereto which is capable ofsupporting CS services. The UTRAN, GERAN, CDMA2000, and the networksimilar thereto may be collectively referred to as a legacy network. Inthe specification and the drawings, presence in one network encompassesboth a case of being connected to one network and a case of camping inone network while staying in an idle state. In addition the term basestation corresponds to an eNB for E-UTRAN. In the specification and thedrawings, the CS security key may represent a whole CS security contextin a broad sense, and may be information including at least one of CK′(or CK), IK′ (or IK), Key Set Identifier (KR), an integrity protectionalgorithm, a start value and a ciphering algorithm. In other words,according to an embodiment of the present invention, the CS security keymay be referred to as CS security key-related information, mean a CSsecurity key itself, or include at least one parameter needed togenerate a CS security key. In addition, the security relatedinformation includes the entirety or a part of a downlink NAS countvalue for a UE.

In the embodiments and drawings of the present invention, an HSS may bean entity identical to or physically concatenated with an HRL.

When an incoming or outgoing voice call occurs while a UE is present inthe E-UTRAN, a CSFB process may be initiated. The UE transmits a requestfor CSFB to an MME through an Extended Service Request message. Then,the MME receiving the message determines whether or not CSFB ispossible, and if CSFB is possible, the MME delivers, to an eNB, anidentifier or Cause indicating that CSFB is needed, through an InitialContext Setup Request message or a UE Context Modification Requestmessage.

Upon receiving the identifier or cause, the eNB delivers a shift command(a handover command or RRC connection release) for CSFB to the UE. Uponreceiving the command, the UE switches to a legacy network supporting aCS service and attempts to access the legacy network.

The CSFB process described above is intended to conceptually describeoperation of 3GPP TS 23.272, and detailed steps thereof may be based onthe 3GPP TS 23.272.

After being connected to the legacy network, the UE needs to transmit alocation registration or service request message to the legacy network.Since the UE does not have security information (e.g., a CS securitykey) to use in a CS network, security (integrity protection orciphering) is not applicable to the location registration or servicerequest message.5

Since a core network (CN) node (MSC or VLR) of the legacy networkreceiving the request message does not have authentication information(e.g., CS security key) about the UE, the CN node may initiate a CS callsetup after additionally performing a process for generatingauthentication information.

However, the security or authentication procedure of the CS networkoccurring in the CSFB process results in increase in the overall time ofCSFB call setup, which may degrade the quality of services provided tothe user.

To solve the problems described above, the present invention proposes amethod for pre-delivering, to a CS CN node, CS security key-relatedinformation (CS security key) which the UE can use after switching tothe legacy network, such that the CS CN node stores the CS securitykey-related information. That is, the present invention provides amethod and apparatus for pre-storing CS security key-related information(a CS security key) in a location registration process between a UE anda CS CN node and using the stored CS security key-related informationwhen CSFB occurs, thereby reducing the call setup time without separatesignaling related to authentication or security.

According to an embodiment of the present invention, when a UE performsa combined attach or combined TAU process in an LTE network, a PS CNnode generates CS security key-related information (a CS security key)in the location registration process and delivers the same to a CS CNnode such that the information is stored. Thereafter, when CSFB occurs,the UE may use CS security key-related information (a CS security key)matching CS signaling in performing CS signaling to proceed with a CSFBprocess without a separate security or authentication procedure.Hereinafter, a detailed description will be given of the process withreference to FIG. 2.

FIG. 2 is a flowchart illustrating a sequence of operations of a UE anda network according to an embodiment of the present invention.

In step S205, a UE 200 transmits, to an MME 210, a combined attach orTAU request message containing a UE identity (e.g., International MobileSubscriber Identity (IMSI), Globally Unique Temporary Identifier (GUTI),or S-TMSI). The combined attach message may be a message making arequest for receiving, for example, a packet exchange service and acircuit exchange service at the same time.

Then, in step S210, the MME 210 delivers, to an HSS 230, a messagerequesting subscription information and authentication information,using the ID of the UE 200. Then, in step S215, the HSS 230 delivers thesubscription information and authentication information (parameter andkey sets related to authentication and security; hereinafter, anauthentication vector) about the UE to the MME 210 in response.

Then, in step S220, the MME 210 may perform the remainingauthentication/security related process together with the UE using thesubscription information and authentication vector information.

According to an embodiment of the present invention, in step S225 in theremaining combined attach or TAU process, the MME 210 generates CSsecurity key-related information (a CS security key). In this case, theMME 210 may generate the CS security key-related information using theauthentication vector received from the HSS 230 or a security contextfor a PS domain, for example, a Kasme key among MM contexts which theMME 210 and the UE have determined to use. Herein, the CS securitykey-related information (CS security key) may include at least one ofCK′ (CK for CSFB), IK′ (IK for CSFB), a Key Set Identifier (KSI), anintegrity protection algorithm, a start value and a ciphering algorithm.

The CS security key-related information also includes the entirety or apart of a downlink NAS count value for the UE. More specifically, theMME and the UE generate the CS security key using the stored Kasme keyand parameters, and the selected NAS count value.

If CSFB or SMS over SGs is applicable for the UE 200, the MME 210performs a location update process together with an MSC/VLR 220 in stepS230. The MME 210 may deliver, to the MSC/VLR 220, anSGsAP-LOCATION-UPDATE-REQUEST message containing the CS securitykey-related information (CS security key).

Upon receiving the message, the MSC/VLR 220 performs locationregistration, and then in S240, delivers an SGsAP-LOCATION-UPDATE-ACCEPTmessage to the MME 210. In this case, if some or all of the CS securitykey-related information (CS security key) delivered by the MME 210 ischanged, the CS security key-related information (CS security key)changed or generated by the MSC/VLR 220 may be included in the message.In the case where some or all of the CS security key-related information(CS security key) is changed, the CS security key-related informationmay contain parameters needed to generate a CS security key as describedabove, and the MME 210 MSC 220 may change and use some of the deliveredparameters even when a specific parameter is delivered to the MSC 220.In this case, the MSC 220 needs to signal the changed CS securitykey-related information (CS security key) back to the MME 210.

Meanwhile, in step S235, the MSC/VLR 220 may store CS securitykey-related information (CS security key) received from the MME 210 orupdated from the received information as a part of the context for theUE 200.

Thereafter, if the attach request for the UE 200 is accepted, the MME210 may deliver, to the UE, an Attach or TAU accept message includingall or some of the information received from MSC/VLR 220 in step S245.Particularly, in this case, if the MSC/VLR 220 changes or generates CSsecurity key-related information (a CS security key) and delivers thesame to the MME 210, the MME 210 may deliver all or some of relevantinformation to the UE. If a downlink NAS count value is used ingenerating a CS security key, and the CS security key needs to begenerated directly by the UE, the MME sends the UE informationcontaining the entirety or a part of the downlink NAS count value.

Thereafter, the UE 200 may perform sense occurrence of the CSFB processin step S255 while performing normal operation in S250. Then, in stepS260, the UE 200 may switch to a legacy network and then generate anddeliver a Location Area (LA) update request or CM service requestmessage. Prior to this process, if the message previously received fromthe MME 210 contains CS security key-related information (a CS securitykey), the UE 200 may use the contained information. Additionally, if thereceived message does not contain the CS security key-relatedinformation (CS security key), the UE 200 may generate CS securitykey-related information (a CS security key). Thereby, the UE 200 mayapply integrity protection to the aforementioned request messages or mayinclude all or some of the CS security key-related information (CSsecurity key) used by the UE, for example, a KSI in the messages. Whenthe UE generates a CS security key from a PS security context, the UEuses the received information, the downlink NAS count information, andthe stored EPS context (i.e., the Kaseme key).

According to the embodiment described above, the UE 200 and the CS CNnode use the CS security key-related information (CS security key)synchronized therebetween, and therefore the remaining CS call setupprocess may be performed without a separate authentication or securityprocedure.

According to another embodiment of the present invention, the CSsecurity key-related information (CS security key) about the UE may bedelivered between CN nodes not in the attach/TAU process but when CSFBactually occurs.

Specifically, if an MME delivers CS security key-related information (aCS security key) to an MSC/VLR while operations are being performedamong a UE, the MME, an eNB, and eNBs of the legacy network, the CS CNnode may retain the CS security key-related information (CS securitykey) before the UE switches to the legacy network to deliver a message.That is, if a process of the MME delivering the CS security key-relatedinformation (CS security key) to the MSC/VLR is performed in parallelwith conventional operation of CSFB according to 3GPP TS 23.272, thesecurity/authentication process needed between the UE and the CS CN nodemay be simplified. Hereinafter, this process will be described in detailwith reference to FIGS. 3 and 4.

FIG. 3 is a flowchart illustrating a sequence of operations of a UE anda network.

Suppose that a UE 300 is attached to (combined with) an LTE networkaccording to 3GPP TS 23.401, 23.272, and CSFB is available to the UE 300in step S305.

In step S310, the UE 300 senses occurrence of outgoing or incoming CSFB.Then, the UE 300 delivers an Extended Service Request message to an MME320 in step S310 to request CSFB.

Then, in step S315, if CSFB is possible, the MME 320 generates CSsecurity key-related information (a CS security key). In this case, theMME 320 may generate the information using a stored authenticationvector or a security context for a PS domain, for example, a Kasme keyamong MM contexts which the MME 320 and the UE 300 have determined touse. Herein, the CS security key-related information (CS security key)may include at least one of CK′, IK′, a Key Set Identifier (KSI), anintegrity protection algorithm, a start value and a ciphering algorithm.

The CS security key-related information also includes the entirety or apart of a downlink NAS count value for the UE. More specifically, theMME and the UE generate the CS security key using the stored Kasme keyand parameters, and the selected NAS count value.

In step S320, the MME 320 may transmit the generated CS securitykey-related information (CS security key) to the MSC/VLR 330 through anSGsAP-SERVICE-REQUEST (in the case of an incoming call) orSGsAP-MO-CSFB-INDICATION (in the case of an outgoing call) message sentto the MSC/VLR 330.

Then, in step S325, the MSC/VLR 330 may store the CS securitykey-related information (CS security key) received from the MME 320 as apart of a context for the UE 340 or may update the CS securitykey-related information (CS security key) based on the informationreceived from the MME 320 when necessary and store the updatedinformation. If the CS security key-related information (CS securitykey) is updated, the MSC/VLR 330 may deliver the updated information tothe MME 320 through a separate SGsAP message in step S330. Since adescription has been given above of the case of updating the CS securitykey-related information (CS security key), a detailed descriptionthereof will be omitted.

In step S335, the MME 320 may deliver a request for execution of CSFB toan eNB 310 by transmitting an identifier or Cause indicating occurrenceof CSFB through an Initial Context Setup Request message (in the idlemode) or a UE Context Modification Request message (in the connectedmode). In this case, the messages may optionally contain CS securitykey-related information (a CS security key) for the UE to use. The CSsecurity key-related information includes the entirety or a part of adownlink NAS count value for the UE. That is, if a downlink NAS countvalue is used in generating a CS security key and the CS security keyneeds to be generated directly by the UE, the MME inserts the entiretyor a part of a downlink NAS count value in the information sent to theeNB.

Then, in step S340, the eNB 310 transmits a response.

Then, in step S345, the eNB 310 delivers, to the UE 300, a command (anRRC connection release or handover command) message to move the UE 300to a legacy network over which a CS service can be provided. If the MME320 delivers CS security key-related information (a CS security key) tothe eNB 310 in the aforementioned process, the eNB 310 may optionallytransmit the received CS security key-related information (CS securitykey) to the UE 300 through the message. In addition, the CS securitykey-related information contains the entirety or a part of a downlinkNAS count value for the UE.

According to an embodiment of the present invention, the sequentialorder of the process of the MME 320 sending a request for execution ofCSFB to the eNB 310 and receiving a response and the process ofdelivering the CS security key-related information (CS security key) tothe MSC/VLR 330 is not important. These processes may be performed inparallel, which will be described in detail with reference to FIG. 4.

Thereafter, in step S355, the UE 345 may switch to the legacy networkaccording to the command of the eNB 310 and then generate and deliver aLocation Area (LA) update request or CM service request message.

Prior to this process, if the message previously received from the eNB310 contains CS security key-related information (a CS security key),the UE 300 may use the contained information in step S350. In addition,if the received message does not contain the CS security key-relatedinformation (CS security key), the UE 300 may generate CS securitykey-related information (a CS security key). Thereby, the UE 300 mayapply integrity protection to the aforementioned request messages usingthe CS security key-related information (CS security key), or may insertall or some of the CS security key-related information (CS security key)used by the UE, for example, a KSI in the messages. When the UEgenerates a CS security key from a PS security context, the UE uses thereceived information, the downlink NAS count information, and the storedEPS context (i.e., the Kaseme key).

According to the embodiment described above, the UE and the CS CN nodeuse the CS security key-related information (CS security key)synchronized therebetween, and therefore the remaining CS call setupprocess may be performed without a separate authentication or securityprocedure.

According to another embodiment of the present invention, the CSsecurity key-related information (CS security key) about the UE may bedelivered between CN nodes not in the attach/TAU process but when CSFBactually occurs. That is, if an MME delivers CS security key-relatedinformation (a CS security key) to an MSC/VLR while operations are beingperformed among a UE, the MME, an eNB, and eNBs of the legacy network,the CS CN node may retain the CS security key-related information (CSsecurity key) before the UE switches to the legacy network to deliver amessage. That is, if a process of the MME delivering the CS securitykey-related information (CS security key) to the MSC/VLR is performed inparallel with conventional operation of CSFB according to 3GPP TS23.272, the security/authentication process needed between the UE andthe CS CN node may be simplified.

FIG. 4 is a flowchart illustrating a sequence of operations of a UE anda network according to another embodiment of the present invention.Suppose that a UE 400 is attached to (combined with) an LTE networkaccording to 3GPP TS 23.401, 23.272, and CSFB is available to the UE 400in step S405. In addition, suppose that outgoing or incoming CSFB hasoccurred to the UE 400.

In this case, in step S410, the UE 400 delivers an Extended ServiceRequest message to an MME 420 to request CSFB. Then, in step S415, ifCSFB is possible, the MME 420 generates CS security key-relatedinformation (a CS security key). In this case, the MME 420 may generatethe information using a stored authentication vector or a securitycontext for a PS domain, for example, a Kasme key among MM contextswhich the MME 420 and the UE 400 have determined to use. Herein, the CSsecurity key-related information (CS security key) may include at leastone of CK′, IK′, a Key Set Identifier (KSI), an integrity protectionalgorithm, a start value and a ciphering algorithm. The CS securitykey-related information also includes the entirety or a part of adownlink NAS count value for the UE. That is, if a downlink NAS countvalue is used in generating a CS security key and the CS security keyneeds to be generated directly by the UE, the MME inserts the entiretyor a part of a downlink NAS count value in information sent to the eNB.

Thereafter, in step S420, the MME 420 may deliver a request forexecution of CSFB to an eNB 410 by transmitting an identifier or causeindicating occurrence of CSFB through an Initial Context Setup Requestmessage (in the idle mode) or a UE Context Modification Request message(in the connected mode). In this case, the messages may optionallycontain CS security key-related information (a CS security key) for theUE 400 to use. The CS security key-related information includes theentirety or a part of a downlink NAS count value for the UE.

Then, in step S425, the eNB 410 transmits a response to the MME 420.Then, in step S430, the eNB 410 delivers, to the UE 400, a message of acommand (an RRC connection release or handover command) to move the UE400 to a legacy network over which a CS service can be provided.

If the MME 420 delivers CS security key-related information (a CSsecurity key) to the eNB 410 in the aforementioned process, the eNB 410may optionally transmit the received CS security key-related information(CS security key) to the UE 400 through the message. In addition, the CSsecurity key-related information contains the entirety or a part of adownlink NAS count value for the UE.

Subsequently, in step S435, the MME 420 may deliver the generated CSsecurity key-related information (CS security key) to the MSC/VLR 430through SGsAP-Service-Request (in the case of an incoming call) orSGsAP-MO-CSFB-Indication (in the case of an outgoing call).

Then, in step S440, the MSC/VLR 430 may store the received CS securitykey-related information (CS security key). Thereafter, the MSC/VLR 430may use the stored information when CS security is needed for the UE400.

In step S450, the UE 400 may switch to the legacy network according tothe command of the eNB 410, and then generate a Location Area (LA)update request or CM service request message and deliver the same to theMSC/VLR 430.

If the message previously received from the eNB 410 contains CS securitykey-related information (a CS security key) before step S450 isperformed, the UE 400 may use the contained information. Additionally,if the received message does not contain the CS security key-relatedinformation (CS security key), the UE 400 may generate CS securitykey-related information (a CS security key). Then, the UE 400 may applyintegrity protection to the aforementioned request messages using thegenerated CS security key-related information, or may insert all or someof the CS security key-related information (CS security key) used by theUE, for example, a KSI in the messages. When the UE generates a CSsecurity key from a PS security context, the UE uses the receivedinformation, the downlink NAS count information, and the stored EPScontext (i.e., the Kaseme key).

According to the embodiment described above, the UE 400 and the CS CNnode use the CS security key-related information (CS security key)synchronized therebetween, and therefore the remaining CS call setupprocess may be performed without a separate authentication or securityprocedure.

Meanwhile, the UE may move during the CSFB process and thus need to setup a call through an MSC/VLR (hereinafter, referred to as MSC2)different from an MSC/VLR (hereinafter, referred to as MSC 1) in whichthe UE has previously been registered. According to another embodiment,if CS security key-related information (a CS security key) about the UEis configured in MSC1, when the MSC is changed to another one during theCSFB process, MSC1 may deliver the CS security key-related information(CS security key) to MSC2 such that a separate security/authenticationinformation exchange process does not occur between the UE and MSC2. Theaforementioned situation will be described with reference to FIG. 5.

FIG. 5 is a flowchart illustrating a sequence of operations between CNnodes.

First, suppose that a combined attach process has been performed inconnection with MSC1 510 in step S505 and thus CSFB has occurred for theUE 500 which can use the CSFB. Additionally, suppose that MSC1 510 hasdelivered CS security key-related information to a UE 500 in step S510.

Suppose that call setup is needed in an area managed by MSC2 520 due tomovement of the UE 500 during the CSFB process as in step S515.

In this case, since the area managed by the MSC has changed, the UE 500transmits an LA update request message to MSC2 520 in step S520. In thiscase, if the UE 500 has CS security key-related information (a CSsecurity key) according to the previous embodiment of the presentinvention, the UE 500 may inset a part of the CS security key-relatedinformation (CS security key), for example, a KSI in the LA updaterequest message and transmit the message or may apply integrityprotection to the LA update request message based on the CS securitykey-related information (CS security key).

Upon receiving the message, MSC2 520 makes a request for location updateto an HLR 530 in step S525 since the UE is not registered therein. Inthis case, the location update request message may contain the number ofthe original MSC for the UE 500, or MSC1 in this embodiment.

Then, the HLR 530 transmits a request for canceling the location to MSC1510 in step S530 using the MSC number. Herein, the message may containthe number of a new MSC for UE 500, or MSC2 in this embodiment.

Upon receiving the message, MSC1 510 inserts the CS security key-relatedinformation (CS security key) stored therein in a PRN message andtransmits the PRN message to MSC2 520 in step S535 to allow a call to beperformed. Thereafter, MSC2 520 and MSC1 510 exchange a PRN response andan IAM message in steps S545 and S550, respectively.

Once MSC2 520 collects all information related to the UE 500, MSC1 510finishes the LA update process together with the UE 500 using thereceived CS security key-related information (CS security key) in stepS555. Then, in step S560, MSC2 520 proceeds with the remaining CSFBprocess.

Hereinafter, a detailed description will be given of a method fordelivering CS security information (a parameter used by an MME ingenerating a CS security key or security key, e.g., downlink NAS count)to a UE when CSFB occurs.

The downlink NAS count is delivered to the UE to meet the followingneed. The UE stores an uplink NAS count value, and the MME stores adownlink NAS count value. The UE and the MME need to estimate the countvalue of the counterpart. If a CS key is to be generated from an EPSsecurity context in order to reduce the time taken for the CSFB, amethod of ensuring that the UE and the MME generate the same key isneeded. If the downlink NAS count is used in generating the CS key, thewhole downlink NAS count value or information (e.g., some bits of thedownlink NAS count) allowing accurate estimation of the downlink NAScount needs to be delivered to the UE in order to increase accuracy ofthe downlink NAS count that the UE estimates.

The first method is to cause an MME to deliver CS security informationto an eNB and cause the eNB to receive the information and deliver thesame to a UE. That is, an MME receiving Extended Service Request forCSFB from a UE delivers CS security information (a generated CS key orparameters for the UE to use in generating a CS key to use whenperforming CSFB, including downlink NAS count) to an eNB through Simessage (Initial UE context setup or UE context modification request)that the MME send to the eNB. The eNB transmits the received CS securityinformation to the UE through an RRC message that the eNB sends to theUE. If CSFB and PSHO Packet Switched Handover are performed at the sametime, the eNB inserts the CS security information (the generated CS keyor parameters for the UE to use in generating a CS key to be used whenperforming CSFB, including downlink NAS count) in an HO command RRCmessage (MobilityFromEUTRA Command) that the eNB sends to the UE. IfCSFB is performed without PSHO, the eNB inserts the CS securityinformation in an RRC message such as an RRC connection release messageor an RRC connection reconfiguration message that the eNB sends to theUE. If the RRC message that the UE receives from the eNB contains the CSsecurity information, the UE proceeds with the CSFB process using the CSsecurity information received from the eNB. If a CS key is contained inthe message, the UE uses the received CS key. If the message contains aparameter for generation of a CS key, for example, the entirety or apart of a downlink NAS count value in place of the CS key, the UEgenerates a CS key using the parameter and proceeds with the CSFBprocess using the generated CS key. If the received message containsonly a part of the downlink NAS count, the UE estimates the wholedownlink NAS count value from the received value and then proceeds withthe remaining process.

The second method is to cause the MME to deliver CS security informationdirectly to the UE through a NAS message. That is, an MME receivingExtended Service Request for CSFB from the UE generates a NAS messagecontaining CS security information (a generated CS key or parameters forthe UE to use in generating a CS key to use when performing CSFB,including downlink NAS count) and delivers the same to an eNB using anSi message (Initial UE context setup, UE context release, or UE contextmodification request) that the MME sends to the eNB. To transmit the NASmessage containing the CS security information to the UE, the MME mayperform a downlink NAS transport process together with the eNB before aprocess of association with the eNB for the general process of CSFB. TheeNB inserts the received NAS message in an RRC message to betransmitted. If the NAS message is contained in an RRC message that theUE receives from the eNB, the UE extracts CS security information fromthe NAS message, and proceeds with the CSFB process using the CSsecurity information. If a CS key is contained in the message, the UEuses the received CS key. If the message contains a parameter forgeneration of a CS key, for example, the entirety or a part of adownlink NAS count value in place of the CS key, the UE generates a CSkey using the parameter and proceeds with the CSFB process using thegenerated CS key. If the received message contains only a part of thedownlink NAS count, the UE estimates the whole downlink NAS count valuefrom the received value and then proceeds with the remaining process.

Meanwhile, since the LTE network cannot support the CS service byitself, technology such as CSFB employing a CS network of 2G/3G may beused when a specific service is needed, as described above.

CSFB uses an interface called SGs to allow exchange of informationbetween an MME and an MSC, but it is difficult to add the SGs interfaceto some MSCs of an operator network. In this case, a method that anoperator having both a LTE network and a 2G/3G network can use tosupport a specific service such as a voice service that is difficult todirectly provide in the LTE network is to allow the UE to directlymonitor control signals of the LTE network and 2G/3G CS network, ratherthan to cause the LTE network to assist in switching the UE to a CSnetwork as in the case of CSFB.

That is, the UE is caused to periodically exchange a control signal withthe 2G/3G network to perform the operation of MM Mobility Management inthe CS network, while transmitting data over the LTE network. Thismethod is referred to as simultaneous GSM and LTE (SGLTE). Particularly,SGLTE using only one radio module will be referred to as Single RadioDual System (SRDS).

Operations of a UE in the idle mode performed in the SRDS when aCS-based service is needed for the UE are shown in FIG. 6.

FIG. 6 is a flowchart illustrating a sequence of operations of a UE inan idle mode performed using SRDS when a CS-based service is needed forthe UE, according to an embodiment of the present invention.

When a CS-based service is needed for a UE 600, the UE 600 switchesdirectly to the 2G/3G network to perform operations to receive theservice as in step S605 without exchanging special control informationwith the LTE system.

In this case, the LTE system (i.e., the Evolved Packet System (EPS))cannot explicitly recognize whether or not the UE 600 has switched tothe 2G/3G network. That is, as indicated in step S610, the LTE systemassumes that the UE 600 is still connected to an eNB 610 of the LTEsystem.

Then, in step S615, a downlink packet for the UE 600 may reach a PGW640. Then, in step S620, the PGW 640 generates charging information, anddelivers the packet to an SGW 630. Then, the SGW 630 transmits aDownlink Data Notification message to an MME 620.

Upon receiving the Downlink Data Notification message, the MME 620 makesa request to the eNB 610 for paging.

However, the UE 600 cannot receive the paging or send a response sincethe UE 600 has already switched to the 2G/3G network in step S605.

Accordingly, the user data packet for which the PGW 640 charges cannotbe transmitted to the UE 600.

If the UE switches to the 2G/3G network to get the CS-based servicewhile staying in the connected mode, the PGW 640 receiving a downlinkpacket generates charging information, and immediately delivers the sameto the eNB 610 through the SGW 630. However, the eNB 610 cannot deliverthe downlink packet to the UE 600, and thus can hardly avoid a situationsimilar to the situation described above.

The present invention proposes a method to solve the aforementionedproblem. Specifically, a UE using the SRDS technology may inform the LTEsystem that the UE will switch to the 2G/3G network, immediately beforethe UE switches to the 2G/3G network to receive a CS-based service.Then, the LTE system receiving this information may deliver informationto a GW to suspend charging the UE or additionally request that downlinkpacket transmission be suspended, so that incorrect charging may notoccur.

Suspension of charging the UE and additional suspension of transmissionof a downlink packet, which is optional, may be released when the UEtransmits a TAU request or Service Request after closing the CS-basedservice and returning to the LTE system.

FIG. 7 is a flowchart illustrating a sequence of operations of a UE andan LTE system according to another embodiment of the present invention.

A CS-based service may be needed for a UE 700 camping in the E-UTRAN,namely an outgoing call is needed or paging for an incoming call may bereceived in step S705.

In this case, in steps S720 and S725, the UE may signal, to the LTEsystem, that the UE will switch to a 2G/3G network soon to receive aCS-based service and cannot receive PS data through the E-UTRAN in themeantime, before the UE switches to the 2G/3G network. This signalingmay be delivered to an MME 720 via an eNB 710 using a specific NASmessage (e.g., EMM status). Such NAS message may contain an IE or Causeindicating the situation, namely indicating that the UE temporarilyswitches to the 2G/3G network to receive the CS-based service. In thepresent invention, delivering the NAS message to the MME via the eNBmeans that an RRC message containing the NAS message generated by the UEis delivered to the eNB through an RRC message, and the eNB receivingthe same delivers the NAS message to the MME through an S1_AP message.

If the UE 700 is in the idle mode, the UE 700 needs to proceed with anRRC connection setup process in steps 5710 and 5715 as shown in thefigure. If the UE 700 is already in the connected mode, the UE 700 mayimmediately transmit the NAS message using an RRC message.

Upon receiving the message, the MME 720 may recognize that the UE 700switches to the 2G/3G network to receive the CS-based service, andcharging for a PS data packet or data transmission should be temporarilysuspended.

Thereby, if the MME 720 has Guaranteed Bit Rate (GBR) bearers for the UE700, the MME 720 performs a process of deactivating/deleting the GBRbearers together with an SGW 730 and a PGW 740 in step S725 and latersteps. In this case, a Delete Bearer Command message delivered to theSGW 730 by the MME 720 in step S730 and delivered to the PGW 740 by theSGW 730 in step S735 may contain an IE or Cause indicating that the UE700 temporarily switches to the 2G/3G network to receive the CS-basedservice.

The MME 720 may also perform a Suspend process to suspend non-GBRbearers. To this end, a Suspend Notification message 5730 delivered tothe SGW 730 by the MME 720 in step S730 and delivered to the PGW 740 bythe SGW 730 in step S735 may contain an IE or Cause indicating that theUE 700 temporarily switches to the 2G/3G network to receive a CS-basedservice.

The PGW 740 deletes the GBR bearers and suspends the non-GBR bearersthrough these processes.

The MME 720 may repeatedly perform these operations for respective PDNconnections. In parallel with the operation with the GWs, the MME 720may transmit, to the eNB 710, a command to release an ECM connection tothe UE 700, namely an S1 UE context release command in step S760.

Upon receiving the command, the eNB 710 may deliver an RRC connectionrelease message to the UE 700 in step S765. Thereafter, according to theembodiment described above, the UE 700 may switch to the 2G/3G networkto proceed with the CS-based service.

According to a variant of the embodiment described above, the UE may notsignal, to the MME, that the UE will switch to the 2G/3G network,through the NAS message. Instead, the UE may deliver the signaling tothe eNB through an RRC message (i.e., a message different from the NASmessage), and the eNB may in turn deliver the same to the MME.

More specifically, the UE may announce, through an RRC message (e.g.,RRC connection request or RRC connection setup complete), that the UEwill switch to the 2G/3G network to proceed with the CS-based service,and then may switch to the 2G/3G network after receiving a response tothe information. Once the eNB receives the information from the UE, theeNB delivers the information to the MME through an S1 AP message.Subsequent operations of the MME and the SGW/PGW are the same as thoseillustrated in FIG. 7.

FIG. 8 is a flowchart illustrating a sequence of operations of a UE andan LTE system performed according to another embodiment of the presentinvention.

First, as shown in the figure, a CS-based service may be needed for a UE800 camping in the E-UTRAN, namely an outgoing call is needed or pagingfor an incoming call may be received in step S805.

In this case, in step S820, the UE 800 may signal, to the LTE system,that the UE 800 will switch to a 2G/3G network soon to receive aCS-based service and cannot receive PS data through the E-UTRAN in themeantime, before the UE 800 switches to the 2G/3G network. Thissignaling may be delivered to an MME 820 using a specific NAS message(e.g., EMM status) as in step S825. Such NAS message may contain an IEor Cause indicating the situation, namely indicating that the UE 800temporarily switches to the 2G/3G network to receive the CS-basedservice.

If the UE 800 is in the idle mode, the UE 800 needs to proceed with anRRC connection setup process in steps S810 and S815 as shown in thefigure. If the UE 800 is already in the connected mode, the UE 800 mayimmediately transmit the NAS message using an RRC message.

Upon receiving the message, the MME 820 may recognize that the UE 800switches to the 2G/3G network to receive the CS-based service, andcharging for a PS data packet or data transmission should be temporarilysuspended. Thereby, the MME 820 may deliver a Release Access BearersRequest message to an S-GW 830 in step S830 to suspend changing the UE800. The message may contain an IE or Cause indicating that the UE 800temporarily switches to the 2G/3G network to receive the CS-basedservice.

Upon receiving the message, the SGW 830 may transmit a Modify BearerRequest message to PGWs 840 having a PDN connection to the UE 800 instep S835. The message may contain a PDN pause ON flag, and additionallycontain an IE or Cause indicating that the UE 800 temporarily switchesto the 2G/3G network to receive a CS-based service. Then, the PGW 840transmits a Modify Bearer Response message to the SGW 830 in step S840.Then, the SGW 830 transmits a Release Access Bearers Response message tothe MME 820 in step S845, and receives a Delete Bearer response messagefrom the MME 820 in step S850. Then the SGW 830 transmits the DeleteBearer Response message to the PGW 840.

In parallel with the operation with the GWs, the MME 820 may transmit,to the eNB 810, a command to release an ECM connection to the UE 800,namely an S1 UE context release command in step S860.

Upon receiving the command, the eNB 810 may deliver an RRC connectionrelease message to the UE 800 in step S865. Thereafter, the UE 800 mayswitch to the 2G/3G network to proceed with the CS-based service.

According to a variant of the embodiment described above, the UE 800 maynot signal, to the MME, that the UE will switch to the 2G/3G network,through the NAS message. Instead, the UE may deliver the signaling tothe eNB through an RRC message (i.e., a message different from the NASmessage), and the eNB may in turn deliver the same to the MME.

More specifically, the UE may inform, through an RRC message (e.g., RRCconnection request or RRC connection setup complete), that the UE willswitch to the 2G/3G network to proceed with the CS-based service, andthen may switch to the 2G/3G network after receiving a response to theinformation. Once the eNB receives the information from the UE, the eNBdelivers the information to the MME through an S1 AP message. Subsequentoperations of the MME and the SGW/PGW are the same as those illustratedin FIG. 8.

When congestion occurs in a Radio Access Network (RAN) (hereinafter,congestion of the RAN indicates congestion of an RAN or specific cellcontrolled by an eNB), it may be preferable to signal this event to acore network (CN) so as to perform optimized traffic processing. Toapply traffic control for each UE, bearer, or service according tocongestion, the CN needs to recognize UEs located in a RAN in whichcongestion is occurring.

More specifically, an embodiment of the present invention takes intoaccount the following situation.

When a RAN node recognizes occurrence of congestion in the RAN andreports occurrence of the congestion to a RAN Congestion AwarenessFunction (RCAF), the RCAF may collect the report and deliver congestioninformation to a PCRF along with an identifier (e.g., cell ID) of thecongested RAN. If the PCRF desires to apply traffic control or policycontrol per UE, user service or bearer, the PCRF needs to recognize UEslocated in the RAN in which congestion is occurring. To this end,according to an embodiment of the present invention, the PCRF deliversthe identifier of the congested RAN to a PCEF (internal function of aPGW). Hereinafter, this term will be interchangeably used with PGW.Then, the PCEF makes a request to the MME for User Location Information(ULI) reporting along with the identifier of the RAN, and the MME maystart ULI reporting on UEs included in the requested RAN.

The LI reporting may occur immediately after the request is made orevery time the location of the UE changes.

FIG. 9 illustrates a method for activating ULI reporting on a UE presentin a specific RAN according to an embodiment of the present invention.

Suppose that a RAN node (which may be an eNB 900 in the figure) hasrecognized occurrence of RAN congestion. Then, the eNB 900 may reportindication information indicating occurrence of congestion to an RCAF910 along with the identifier (e.g., cell ID) of the RAN in whichcongestion has occurred.

Then, the RCAF 910 may collect the information and deliver thecongestion information to a PCRF 920 along with the identifier (e.g.,cell ID) of the RAN in which congestion has occurred.

If the PCRF 920 desires to apply traffic control or policy control eperUE, user service or bearer, the PCRF 920 needs to recognize UEs locatedin a RAN in which congestion is occurring. To this end, the PCRF 920 maydeliver, to a PCEF 930, a request message for making a request foractivating ULI reporting on UEs located in a specific RAN.

The message may include an identifier of the RAN (e.g., Cell ID) andinformation on time (e.g., a time value) for which the request is valid.

Upon receiving the request, the PCEF 930 may transmit, to S-GWs 940, arequest message for making a request for activating ULI reporting. Thisrequest message may also include an identifier of the RAN (cell ID) andinformation on time (e.g., a time value) for which the request is valid.

Upon receiving the message, the S-GW 940 may deliver the information toMMEs 950. The MME 950 receiving the information recognizes UEs locatedin the requested RAN, and starts ULI reporting on the UEs.

If the request message contains time information, ULI reporting isallowed to be applied only for the time, and is deactivated aftersending a ULI report as soon as a specific UE leaves the requested RAN.

According to another embodiment of the present invention, theaforementioned problem may be solved if the PCRF delivers, to the PCEF,the identifier of a RAN in which congestion has occurred, and the PCEFobtains a list of UEs located in the RAN, and then activates ULIreporting on the UEs. The ULI reporting may be performed when a requesttherefor is received or every time the location of the UE changes.

FIG. 10 illustrates a method for activating ULI reporting on a UEpresent in a specific RAN according to another embodiment of the presentinvention.

Suppose that a RAN node (which may be an eNB 1000 in the figure) hasrecognized occurrence of RAN congestion. Then, the eNB 1000 may report,to an RCAF 1010, indication information indicating that congestion hasoccurred along with an identifier (e.g., Cell ID) of a RAN in whichcongestion has occurred.

Then, the RCAF 1010 may collect the information and deliver thecongestion information to a PCRF 1020 along with the identifier (e.g.,cell ID) of the RAN in which congestion has occurred.

If the PCRF 1020 desires to apply traffic control or policy control perUE, user service or bearer, the PCRF 1020 needs to recognize UEs locatedin the RAN in which congestion is occurring. To this end, the PCRF 1020may deliver, to a PCEF 1030, a request message for making a request foractivating ULI reporting on UEs located in a specific RAN. The requestmessage may contain an identifier of the RAN (e.g., Cell ID) andinformation on time (e.g., a time value) for which the request is valid.

Upon receiving the request, the PCEF 1030 may transmit, to S-GWs 1040, amessage for making a request for a list of UEs belonging to the RANincluding the identifier of the RAN. The request message may contain aperiod of reporting the list of UEs and information on time (e.g., atime value) for which the request is valid.

Upon receiving the request message, the S-GW 1040 may deliver theinformation to MMES 1050. The MME 1050 receiving the information mayrecognize UEs located in the requested RAN, and create a list ofidentifiers of the UEs. Then, the MME 1050 may deliver the created listto the S-GW 1040 through a message sent to the S-GW 1040.

Reporting such list of UEs may periodically occur if the request messagedelivered via the S-GW 1040 includes a period. In addition, if a validtime is included in the request message, the reporting may be applieduntil the valid time expires. The list of UEs created and reported bythe MME 1050 may be finally delivered to the P-GW (PCEF) 1030 via theS-GW 1040. The PCEF 1030 may recognize UEs included in the congested RANbased on the information, and also dynamically activate ULI reporting torecognize the position information on the UEs.

According to another embodiment of the present invention, theaforementioned problem may be solved using another method. Morespecifically, when the PCRF delivers, to the PCEF, the identifier of theRAN in which congestion has occurred, the PCRF may make a request forreporting RAN Congestion Information (RCI) via GTP (GPRS TunnelingProtocol)-C/GTP-U, and the PCEF may make a request to a RAN node for RCIreporting on the UEs belonging to the RAN. Thereby, the problem may besolved.

The activated RCI reporting may be performed immediately after therequest is received or every time the location of a UE changes, and maybe terminated when a specific UE moves to an uncongested RAN.

FIG. 11 illustrates a method for activating RCI reporting on a UEpresent in a specific RAN according to another embodiment of the presentinvention.

A RAN node (which may be an eNB 1100 in the figure) recognizesoccurrence of RAN congestion, and reports, to an RCAF 1110, informationindicating that congestion has occurred along with an identifier (e.g.,Cell ID) of a RAN in which congestion has occurred.

Then, the RCAF 1110 may collect the information and deliver thecongestion information to a PCRF 1120 along with the identifier (e.g.,cell ID) of the RAN in which congestion has occurred. If the PCRF 1120desires to apply traffic control or policy control per UE, user serviceor bearer, the PCRF 1120 needs to recognize UEs located in the RAN inwhich congestion is occurring, and additionally needs to recognize morespecific congestion information for each user/bearer/service.

To this end, the PCRF 1120 may deliver, to a PCEF 1130, a requestmessage for making a request for activating RCI reporting on UEs locatedin a specific RAN. The message may contain an identifier of the RAN(e.g., Cell ID) and information on time (e.g., a time value) for whichthe request is valid. The RCI may include identifiers of the UEs, a RANidentifier, congestion state information (a congestion level, occurrenceof congestion, etc.).

Upon receiving the request, the PCEF 1130 may deliver a message formaking a request for activating RCI reporting on UEs present in the RAN,using a GTP-C message. This request may include valid time informationand a reporting period mentioned above.

The request is delivered from the PCEF 1130 to a S-GW 1140 via the GTP-Cmessage, and is in turn delivered from the SGW 1140 to an MME 1150.Then, the MME 1150 may insert the information in an S1AP messagetransmitted to the RAN node. In particular, the MME 1150 may use thereceived RAN identifier to transmit, only to a RAN matching theidentifier, a request for starting RCI reporting.

The RAN node receiving the message may recognize UEs located in therequested RAN, and start RCI reporting on the UEs. If the requestmessage contains time information, the RCI reporting is allowed to beapplied only for the time, and is deactivated after sending a last RCIreport as soon as a specific UE leaves the requested RAN.

Such RCI may use a user data packet (e.g., GTP-U header or IP header)transmitted on uplink, or may be inserted in a separate S1-AP message(when the eNB delivers the RCI to an MME) and a GTP-C message (when theMME delivers the RCI to an S-GW, and the S-GW delivers the same to aP-GW).

The embodiment described above includes a process of a one network node(e.g., RAN Congestion Awareness Function (RCAF)) making a request toanother network node (e.g., an MME) for information for determining UEslocated in a congested cell and receiving the information.

In addition, in the embodiment described above, description has beengiven of a situation in which messages are delivered via intermediatenodes (a PCRF, a PGW, or an SGW) when one network node makes a requestfor information to another network and receives a response.

It should be noted that main points of the embodiments described abovemay also be applied to a case where a direct connection (a referencepoint or an interface) is established between one network node andanother network node, and messages are directly transmitted and receivedtherebetween without an intermediate node.

Hereinafter, a detailed description will be given of another embodimentof the present invention described above, namely, an embodiment in whichone network node has a direct connection to another network node anddirectly transmits and receives a message, with reference to thedrawings.

FIG. 12 is a flowchart illustrating an operation of exchanging a messagebetween two network nodes to identify UEs located in a congested cellaccording to an embodiment of the present invention.

A network node (hereinafter, an RCAF 1220) needs to identify UEs locatedin a specific cell (or eNB). This need may occur when the network noderecognizes occurrence of congestion in the specific cell (or eNB), or aspecific condition (e.g., a certain time unit) is satisfied.

As shown in FIG. 12, the RCAF 1220 may transmit, to another network node(hereinafter, an MME 1210), a request message for requesting UEinformation in step S1210. The message may be a UE information requestor IMSI/APN information request message. The message may include anidentifier for identifying a selected area. The area identifier may be aCell ID or an eNB ID. The message may additionally include an identifierfor identifying a selected operator, for example, a selected PLMN ID. Ifa RAN is shared by multiple operators, the operator identifier (PLMN ID)may be used to receive information on a UE registered in a specificoperator. The message may be a request message employing a Diameterprotocol. In this case, the identifier for identifying the selected areamay be included in the message as a part of Attribute-Value-Pair (AVP).

The MME 1210 may transmit a response message to the RCAF 1220 in stepS1220. The message includes an ID list of UEs located in the selectedarea (cell, eNB) included in the request message. The IDs foridentifying the UEs may be IMSIs. If the request message received in theprevious step includes the selected PLMN ID, the MME may include onlyUEs registered in the selected PLMN (i.e., only UEs for which theselected PLMN or registered PLMN is identical to the requested PLMN) inthe list. In addition, the UE information may include a registered PLMNID of the UE.

In this case, the MME 1210 may perform a separate location reportprocess together with an eNB in order to identify UEs located in aspecific area. The aforementioned message may be a response messageusing the Diameter protocol, for example, a UE information response orIMSPAPN information response message, and the user ID information may beincluded in the message as a part of AVP.

The RCAF 1220 may identify UEs located in an area in which congestionhas occurred, using the received information. When necessary, the RCAF1220 may use the information in determining UE congestion information(RAN congestion information) to be delivered to another network node(e.g., a PCRF).

Meanwhile, if congestion control is applied only to a specific service,exchanging congestion information on UEs having other services may notonly cause unnecessary signaling, but also increase processing load innetwork nodes. For example, if a main cause of congestion occurring in anetwork is traffic transmitted and received through an EPS bearer usingQoS Class Identifier (QCI) 9 or 6, and congestion control is applied tothe traffic, it is not necessary to deliver congestion information on aUE having another EPS bearer, for example, a UE having only an EPSbearer using QCI 5. That is, the RCAF 1220 may determine whether or notto deliver congestion information based on a combination of one or moreinformation items (APN, QCI, ARP) of a UE received from the MME 1210,thereby reducing unnecessary signaling and processing load.

FIG. 13 is a flowchart illustrating an operation of exchanging a messagebetween two network nodes to identify UEs located in a congested cell(or eNB) and information on a PDN connection of each UE.

A network node (hereinafter, an RCAF 1320, which is a node to collectcongestion information and deliver the same to another node) needs toidentify information on UEs located in a specific cell (or eNB). Thisneed may occur when the network node recognizes occurrence of congestionin the specific cell (or eNB), or a specific condition (e.g., a certaintime unit) is satisfied.

The RCAF 1320 may transmit, to another network node (hereinafter, an MME1310), a request message for requesting UE information in step S1310.The message may be a UE information request or IMSI/APN informationrequest message. The message may include an identifier for identifying aselected area. The area identifier may be a Cell ID or an eNB ID. Themessage may additionally include an identifier for identifying aselected operator, for example, a selected PLMN ID. If a RAN is sharedby multiple operators, the operator identifier (PLMN ID) may be used toreceive information on a UE registered in a specific operator. Themessage may be a request message employing a Diameter protocol. In thiscase, the identifier for identifying the selected area may be includedin the message as a part of AVP.

The MME 1310 may transmit a response message to the RCAF 1320 in stepS1320. The message includes an ID list of UEs located in the selectedarea (cell, eNB) included in the request message and a list of UEinformation. The IDs for identifying the UEs may be IMSIs, and UEinformation for each IMSI may be included in the message. If the requestmessage received in the previous step includes the selected PLMN ID, theMME may include only UEs registered in the selected PLMN (i.e., only UEsfor which the selected PLMN or registered PLMN is identical to therequested PLMN). In addition, the UE information may include aregistered PLMN ID of the UE.

In particular, the UE information may be PDN connection or EPSbearer-related information, and an APN, a QCI of an EPS bearer and anARP of the EPS bearer may be used as the information.

If the EPS bearer information is used, the selected EPS bearer may be adefault bearer of the PDN connection. If the UE has two or more PDNconnections or two or more EPS bearers, the message may contain allinformation for each PDN connection or EPS bearer.

Meanwhile, the MME 1310 may perform a separate location reportingprocess together with an eNB in order to identify UEs located in aspecific area. The aforementioned message may be a response messageusing the Diameter protocol, for example, a UE information response orIMSPAPN information response message, and the user ID information andthe UE information may be encoded using AVP and included in the message.

The RCAF 1320 may identify UEs located in an area in which congestionhas occurred, using the IDs of UEs in the received information. Whennecessary, the RCAF 1320 may use the IDs of UEs in determining UEcongestion information (RAN congestion information) to be delivered toanother network node (e.g., a PCRF).

The RCAF 1320 may select a PCRF proper for each UE using APNs used byUEs in the received information. The RCAF 1320 may control delivery ofcongestion information using the EPS bearer information (QCIs or ARPs)used by UEs in the received information. That is, the RCAF 1320 maydetermine whether or not to transmit congestion information to anothernetwork node (e.g., the PCRF) and a transmission period, using the EPSbearer information (QCIs or ARPs) used by UEs in the receivedinformation.

For example, if a QCI of an EPS bearer of a UE has a specific value(e.g., QCI 9 or QCI 6), the RCAF 1320 may deliver the congestioninformation to the PCRF. Otherwise, the RCAF 1320 may not deliver thecongestion information.

Alternatively, the RCAF 1320 may use APN information in determiningwhether or not to deliver the congestion information to the PCRF. Forexample, if the APN information is an APN for a well-known IMS serviceor VoLTE, the RCAF 1320 may not deliver the congestion information.Alternatively, if the APN information is an APN for best effort or atypical Internet service, the RCAF 1320 may deliver the congestioninformation. Of course, the RCAF 1320 may determine whether or not todeliver the congestion information to the PCRF based on a combination ofAPN, QCI and ARP information.

If UEs located in a congested cell do not change, or UE information doesnot change, exchange of a message between the RCAF and the MME mayresult in unnecessary signaling and increase in processing load.

According to an embodiment of the present invention, the RCAF maysubscribe UE information reporting (or notification) to an MME alongwith a notification condition, and the MME may report UE information tothe RCAF when the notification condition is satisfied, even if the RCAFdoes not request the UE information. Thereby, unnecessary messageexchange may be prevented, and processing load in the RCAF may bereduced.

FIG. 14 is a flowchart illustrating a message exchange process foractivating notification to periodically receive UE information.

A network node (hereinafter, an RCAF 1420, which is a node to collectcongestion information and deliver the same to another node) registersnotification for receiving information on UEs located in a specific cell(or eNB). This operation may be performed when the network noderecognizes occurrence of congestion in the specific cell (or eNB), or aspecific condition (e.g., a certain time unit) is satisfied.

The RCAF 1420 may transmit, to another network node (hereinafter, an MME1410), a request message for registering UE information notification instep S1410. The message may be a Subscribe Notification Request message.The message may include an identifier for identifying a selected area.The area identifier may be a Cell ID or an eNB ID. The message mayadditionally include an identifier for identifying a selected operator,for example, a selected PLMN ID. If a RAN is shared by multipleoperators, the operator identifier (PLMN ID) may be used to receiveinformation on a UE registered in a specific operator.

The message may further include an identifier for identifying a selectedUE. In particular, an IMSI may be used as the identifier.

The message may further include time information indicating a time forwhich a notification request is valid or a time at which the requestednotification operation expires.

The message may also include conditions for performing the notificationoperation such as, for example, a time period of occurrence ofnotification when periodic notification is needed, or a condition thatinformation on a UE located in a selected area changes (e.g., a new UEenters the selected area or an existing UE moves out to another area).

The message may be a request message using the Diameter protocol. Inthis case, the information or the conditions are encoded using AVP.

Then, the MME 1410 may configure notification in step S1420, andtransmit a response message to an RCAF 1430 in step S1430. In this case,a message indicating that notification has been registered may be aSubscribe Notification Answer message using the Diameter protocol.

Thereafter, the MME 1410 determines whether to perform the notificationoperation according to the configured notification information, andperforms a notification process together with the RCAF 1420 if theconditions are met.

If an expiration condition for the notification operation is receivedfrom the RCAF 1420 in the notification configuration process, the MME1410 perform notification only by the notification operation expirationtime.

If a notification condition is included in the notificationconfiguration process, the MME 1410 performs notification only if thenotification condition is satisfied.

A message used for notification may contain a list of UE IDs and UEinformation. The IDs for identifying the UEs may be IMSIs, and UEinformation for each IMSI may also be contained in the message. If therequest message received in the previous step includes a selected PLMNID, the MME may include only UEs registered in the selected PLMN (i.e.,only UEs for which the selected PLMN or registered PLMN is identical tothe requested PLMN) in the list. In addition, the UE information mayinclude a registered PLMN ID of the UE.

Herein, the UE information that the MME 1410 delivers to the RCAF 1420may include only information on UEs changed after the informationtransmitted to the RCAF for the last time, or include information on allUEs located in the selected area.

If the MME 1410 transmits only updated information to the RCAF 1420, theRCAF 1420 may update, delete or add a part of the information storedtherein using the updated information.

If the MME 1410 transmits information on all UEs located in the selectedarea to the RCAF 1420, the RCAF 1420 replaces the information storedtherein with the received information.

Meanwhile, the message may be a response message using the Diameterprotocol, for example, a Push Notification Answer message, the UE IDinformation and the UE information may be encoded using AVP and includedin the message.

FIG. 15 is a block diagram illustrating the internal structure of a UEaccording to an embodiment of the present invention. As shown in FIG.15, the UE of the present invention may include an RF transceiver 1510,a storage unit 1520, and a controller 1530.

The RF transceiver 1510 serves to transmit and receive data for wirelesscommunication of the UE. The RF transceiver 1510 may include an RFtransmitter to up-convert and amplify the frequency of a transmittedsignal and an RF receiver to low-noise amplify a received signal anddown-convert the frequency of the signal. The RF transceiver 1510 mayreceive data over a radio channel, output the data to the controller1530, and transmit data output from the controller 1530 over a radiochannel.

The storage unit 1520 stores a program and data which are needed foroperation of the UE.

The controller 1530 controls signal flows between blocks such that theUE can operate according an embodiment of the present invention. Forexample, when the controller 1530 senses CSFB triggering, the controller1530 may check CS security key-related information. The controller 1530may also control a call setup process for a CS domain based on the CSsecurity key-related information such that the process is performed.

In addition, the controller 1530 may control a series of processes forchecking CS security key-related information transmitted from a CN nodeof the mobile communication system. The controller 1530 may also controlthe UE to generate the CS security key-related information from PSsecurity key-related information that the UE has used in a securityprocedure for a packet exchange domain.

In addition to the embodiment given above the controller 1530 maycontrol the UE such that the UE operates according to another embodimentof the present invention.

FIG. 16 is a block diagram illustrating the internal structure of a CNnode according to an embodiment of the present invention. As shown inFIG. 16, a CN node of the present invention may include an interfaceunit 1610, a storage unit 1620, and a controller 1630. In this case, theCN node may include an MME.

The interface unit 1610 may serve to perform signal processing for wiredcommunication of the CN node.

The storage unit 1620 stores a program and data which are necessary foroperation of the CN node.

The controller 1630 controls signal flows between blocks such that theCN node can operate according to an embodiment of the present invention.For example, the controller 1630 may generate security key-relatedinformation for the UE to use in a circuit switched fallback, (CSFB)procedure. In addition, the controller 1630 may control to transmit thegenerated CS security key-related information to a control node (e.g.,MSC/VLR) of the CS domain. In this case, the controller 1630 may controlgenerate the CS security key-related information in the process ofregistration of the UE in the packet exchange domain or at the time anextended service request message transmitted from the UE according totriggering of CSFB in the UE is received.

In addition, the controller 1630 may transmit the CS securitykey-related information to the UE. In addition, if changed CS securitykey-related information is received from the control node of the CSdomain, the controller 1630 may control to transmit the received changedCS security key-related information to the UE.

If the CN node is an RCAF, the controller 1630 may control to receivecongestion related information from at least one eNB.

In addition, the controller 1630 may control to transmit, to the MME, aUE information request message for requesting information on a UEcorresponding to the eNB, based on the congestion related information,and to receive a UE information response message containing informationon the UE corresponding to the eNB from the MME.

The controller 1630 may transmit the information on the UE correspondingto the eNB to another CN node.

In this case, the controller 1630 may control to transmit the UEinformation request message directly to the MME or transmit the UEinformation request message to the MME via at least one CN node. The UEinformation request message may contain an identifier for identifying arequested area, and the identifier may include at least one of a cell IDand eNB ID. The UE information response message may contain a list ofUEs served by the eNB, and the identifier for identifying the UE mayinclude an International Mobile Subscriber Identity (IMSI).

If the core network node is an MME, the controller 1630 may receive,from the CN node, a UE information request message for requestinginformation corresponding to at least one eNB in which congestion hasoccurred. Then, the controller 1630 may check information on a UEcorresponding to the eNB, and transmit, to the core network, a UEinformation response message containing information on the UE.

In the above-described embodiments, all steps may be selectivelyperformed or part of the steps and may be omitted. In each embodiment,the steps are not necessarily performed in accordance with the describedorder and may be rearranged.

The messages need not always be transmitted in order and transmissionorders of the messages may be changed. The steps and messagetransmission operations may be independently performed

Hereinabove, various embodiments of the present invention have beenshown and described for the purpose of illustration without limiting thesubject matter of the present invention. It should be understood bythose skilled in the art that many variations and modifications of themethod and apparatus described herein will still fall within the spiritand scope of the present invention as defined in the appended claims andtheir equivalents.

1.-20. (canceled)
 21. A method for controlling congestion by a corenetwork node in a mobile communication system, the method comprising:receiving congestion information; transmitting, to a mobility managemententity (MME), a first message for requesting user equipment (UE)information, based on the congestion information, the first messageincluding at least one of an identifier of a congested base station oran identifier of a congested cell; receiving, from the MME, a secondmessage including the UE information, the UE information including alist of at least one UE corresponding to the congested base station orthe congested cell, the list of the at least one UE being determinedbased on a location report procedure between the MME and the congestedbase station or the congested cell.